The former News International chief executive "fostered" the animal after it retired from active service.

She paid for food and vet bills until it was rehoused with a police officer in 2010 - months before fresh investigations into illegal activities at the News of the World.

Confirmation of the two-year loan comes amid ongoing scrutiny over the close relationship between police and the media giant.

A Metropolitan Police spokesman said Ms Brooks was first given permission to take charge of the horse in 2008. "When a police horse reaches the end of its working life, mounted branch officers find it a suitable retirement home," he said.

"Whilst responsibility for feeding the animal and paying vet bills passes to the person entrusted to its care at its new home, the horse remains the property of the Metropolitan Police Service.

"Retired police horses are not sold on and can be returned to the care of the MPS at any time. In 2008 a retired MPS horse was loaned to Rebekah Brooks. The horse was subsequently re-housed with a police officer in 2010."

Ms Brooks, 43, remains on bail after being questioned by detectives last summer on suspicion of phone hacking and corruption. The keen rider is married to racehorse trainer Charlie Brooks.

The horse borrowed by Ms Brooks was one of 12 retired by the force in 2008. A further 29 had their duties ended between 2009 and 2011. Many of the animals are retired with The Horse Trust charity in Buckinghamshire.

Ms Brooks was arrested and questioned in July, days after resigning as chief executive. Metropolitan Police figures showed that there were 829 potential victims of phone hacking, of whom 231 were said to be uncontactable.